Assembly.LoadFrom(assemblypath) in WCF Servicefactory - wcf

Question

I am using a WCF ServicehostFactory for my wcf service in conjunction with unity for service and repository/DAL instantiation using interfaces.
I want to load an assembly into my appdomain (before the service is instantiated), whose types are registered in my web.config for Unity DI.
<assembly name="Customer.DAL.AdventureWorks"/>
<assembly name="Customer.DAL.Blogger"/>
<assembly name="Customer.Interfaces"/>
<assembly name="Customer.DAL"/>
<namespace name="Customer.Interfaces.Repository"/>
<namespace name="Customer.DAL.AdventureWorks"/>
<namespace name="Customer.DAL.Blogger"/>
<container>
<register type="Customer.Interfaces.DAL.IDal, Customer.Interfaces" mapTo="Customer.DAL.API, Customer.DAL">
<lifetime type="transient"/>
</register>
<register type="Customer.Interfaces.Repository.IRepositoryDepartment, Customer.Interfaces" mapTo="Customer.DAL.AdventureWorks.RepositoryDepartment, Customer.DAL.AdventureWorks">
<lifetime type="transient"/>
</register>
<register type="Customer.Interfaces.Repository.IRepositoryBlogs, Customer.Interfaces" mapTo="Customer.DAL.Blogger.RepositoryBlogs, Customer.DAL.Blogger">
<lifetime type="transient"/>
</register>
</container>
and I am using the following code to load the assembly:
Assembly.LoadFile("C:\xxxxx\Customer.DAL.dll"); // loaded from somewhere on disk.
I have verified the existence of the loaded assembly against the current appdomain and the assembly is loaded successfully.
Immediately after that, I try to register the service type using unity, but I get the following exception:
The type name or alias Customer.DAL.API, Customer.DAL could not be resolved. Please check your configuration file and verify this type name.
So why can the type "Customer.DAL.API" not be resolved?
EDIT: I run FusionLog in parallel and it traces out the failed assembly binding.
Why does it actually search for the assembly, cause the this assembly has already been loaded by me using reflection as mentioned above?!
EDIT-II:
#Tuzo:
I read all the articles you posted.
And tried the following:
static Assembly CurrentDomain_AssemblyResolve(object sender, ResolveEventArgs args)
{
AssemblyName asname = AssemblyName.GetAssemblyName(#"C:\xxxx\KM_Solution\Customer.DAL\bin\Debug\Customer.DAL.dll");
return Assembly.Load(asname);
}
But I still get the exception. I checked AppDomain.CurrentDomain.GetAssemblies() and I can find my assembly, but it still throws the exception that Unity cannot resolve the type...

Answer 1

I would handle the AssemblyResolve event and load the assembly if you need to:
AppDomain.CurrentDomain.AssemblyResolve += CurrentDomain_AssemblyResolve;
IUnityContainer container = new UnityContainer()
.LoadConfiguration();
// Example of resolving without hard reference
var customerDal = container.Resolve(
Type.GetType("Customer.Interfaces.Repository.IRepositoryDepartment, Customer.Interfaces"));
private static Assembly CurrentDomain_AssemblyResolve(object sender, ResolveEventArgs args)
{
string assemblyName = #"C:\xxxxx\" + args.Name + ".dll";
if (File.Exists(assemblyName))
{
return Assembly.LoadFile(assemblyName);
}
return null;
}
In terms of why LoadFile doesn't work, the reason is the Load Context. There are 3 contexts: Load, LoadFrom, and Neither. When you use LoadFile or Load(byte[]) then the assembly is loaded into the Neither context. In the neither context nothing can bind to the assembly without using AssemblyResolve.
See:
Understanding The CLR Binder
Best Practices for Assembly Loading
Suzanne Cook's Blog: Choosing a Binding Context and LoadFile vs. LoadFrom